The present invention relates to fiber optic arrays and more particularly to large, matrix configured arrays and the method and tools for making the same.
Fiberoptics has been the driving force in the communication revolution which has enabled carriers to achieve enormous data throughput. In order to realize the full potential of the technology, fiberoptics will be incorporated into every facet of the integrated electronics, which will then make it possible to fully utilize the enormous bandwidth of the optical fiber with the high speeds of the semiconductor integrated circuitry.
To this end, arrays of optical fibers need to be coupled precisely and reliably to semiconductor laser and detector arrays on a chip. Already, various groups throughout the world have demonstrated feasibility of high speed optoelectronic VLSI switching and two dimensional fiberoptic arrays for an optical crossbar switch.
In 1996, reports were published of achieving approximately + or xe2x88x92 5 micrometer fiber positional accuracy. In June 1997, Messrs. J. Sherman et al. filed and obtained on May 25, 1999 U.S. Pat. No. 5,907,650 by Fiberguide Industries, Inc. relating to a new method and array achieving at least + or xe2x88x92 2 micrometer fiber positional accuracy.
Although these advances in the art enhance the accuracy and reliability of fiber arrays, they introduce or amplify other technical problems that must be solved to satisfy industry""s need for large number, reliable, high precision, fiber matrix arrays. For example, as the demand for the number of fibers in matrix arrays increases, from 8xc3x978 just a few years ago to the present more than 60xc3x9760, assembly problems arise because of the difficulty in handling and positioning and securing the large number of fibers in the assembly.
A primary object of the present invention is to provide new connector apparatus, tools and methods of assembly that solve the aforementioned problems, provide an efficient and reliable manufacturing method for such large element number arrays and produce such a fiber array connector matrix with highly accurate and reliable fiber placement that is sufficiently robust for further installation and use in the field.
Another primary object of the present invention is to provide such an optical array with enhanced precision compared to the known prior art, which can be effectively and efficiently manufactured, with lower unit costs than currently available products. One feature of this aspect of the invention is to provide a mating mask material with fiber mounting openings that are photo etched or otherwise precisely formed in predetermined patterns, such as rows and columns.
According to another primary object of the present invention, the jackets and buffer layers of fibers are stripped and the distal fiber ends are inserted through the openings and bonded to the mask. In a preferred embodiment, the fiber tip is conically shaped according to the principles of U.S. Pat. No. 5,907,650. The conical surface cooperates with the mask opening, as, e.g., described below, to enable more accurate fiber positioning. By conically shaping the fiber ends the insertion of the fiber into mask opening can be self limiting by having the fiber bottom against the mask opening side walls.
An exemplary embodiment according to principles of the present invention, includes an elongated housing or body securing a forward mask which defines a large number of mask openings arranged in a predetermined pattern, such as 60 rows by 60 columns or more. The connector housing serves several functions. The most important function is to provide protection and stability for the fibers. The connector also serves as the mechanical interface from the array assembly to the final instrument, and protects the fibers and the final instrument from the environment. This connector is designed to be hermetically sealed after the array is assembled.
The silicon wafer is etched with holes at designated centers, and because of the hole manufacturing process, the location of the hole centers can be held to extreme precision such as a tenth of a micron for 120-200 micron holes. The holes can be tapered to create a mating surface to both position the fiber and a bottoming wall surface for the tapered fibers to seat against. The mask wafer also has a series of holes that provide alignment for guide plate assembling and alignment to the connector.
The housing internal chamber defines precise guide elements to cooperate with a series of guide plates. Each guide plate forms a series of fiber guide channels or grooves that mate up with the holes in the silicon wafer. The guide plates are stacked within the housing so that the bottom of one guide plate acts as a cover for the channels of another guide plate. Preferably, the forward edges of each stacked plate rests flush against the rear of the array mask or rear of a guide mask if one is used. The grooves provide a guide for the fibers to slide in as the fibers are being inserted into the wafer. Fibers can be tool inserted as one group, such as a row of fibers, at a time. The grooves guide each group of fibers into their designated holes in the wafer mask. The covered grooves in the guide plates also keep the fibers perpendicular to the wafer front surface, and they provide protection to the stripped fibers as described below. The guide plates also minimize the amount of epoxy needed in the assembly, which creates a low stress termination for the fibers in the mask. The array assembly is designed to be used with any type of optical fiber provided the fiber geometry can fit within the specified hole center-to-center spacing. The guide plate is also designed with two alignment holes on the back of the plate that mate up with the alignment pins on the assembling or fiber insertion tooling.
One exemplary embodiment of insertion tooling is designed to hold at least one row or column of optical fibers at a time. The fiber tips in the tooling are held at the same center-to-center spacing as the grooves in the guide plates. The insertion tool is made up of four parts, a grooved guide section and a grooved insertion section that make up the main part of the tool and two lids or tool covers that keep fibers in these sections. The front guide section of the tool is movable to and away from the back insertion section of the tool. The back section of the tool holds tight to each fiber jacket allowing the fiber to be positioned to a prescribed position and held there. The grooved front section of the tool can slide longitudinally along the fibers that are held by the back section of the tool. The fiber distal end portions can be etched and shaped while held in the tool. After the fibers are etched the front section is moved forward covering and protecting the tips of the fibers. An injection needle or other applicator can be used to apply liquid epoxy to the rear of the guide plate channels in the row desired for insertion. The tool is then mated to the respective guide plate while the fiber tips remain covered. The front section mates with one guide plate row of channels defined by the mated guide plate. When the tool is in place, the back insertion section is moved forward toward the front section. In response, the fibers are moved out of the front section into the guide plate channels and are wetted by the liquid epoxy therein. The fibers continue to advance along the channels until the fibers bottom on the mask holes with the fiber tips extending through the respective mask holes and the conical fiber tip surfaces engaging or bottoming on the hole walls or edges. The operator or system checks to assure that all fiber tips in the row penetrate through and bottom in the mask holes. Thereafter, the tool lids are removed from the tool. This releases the fibers from the tool. The tool can then be lifted off of and away from the fibers.
The tool is subsequently loaded with another row or column of fibers. This process is repeated until all of the guide plates are loaded with fibers and all fiber tips extend through all of the openings. The stacked guide plates enhance the securement of all fibers and greatly add to the strength and integrity of the assembly.
After cure, it is preferred to bond the housing aft sidewalls and cover in place and apply a layer of epoxy to cover the mask front surface and protruding fiber tips. Next, it is preferable to position the housing vertically with the forward mask downward and liberally apply (pour) silicone, epoxy or other suitable material into the housing chamber through the open aft housing end. This liquid bonding material will tend to fill empty spaces around the mask, cladded fiber cores, guide plates, and other elements and fiber parts including the jacketed fiber portions within the housing. Once cured, the assembly has great strength, needs no further strain relief device for reliability, and prevents moisture accumulation within the housing.
It is then preferable to grind and/or polish the epoxy, cladded core tips, and the forward mask to produce a precise planar matrix surface with fiber cores diameter flush against this planar forward mask face surface. If desired, the housing aft end can be fitted with a further strain relief, bundling, or protective device to cooperate with the exposed, jacketed fibers exiting the housing.
In an alternate embodiment, the mask and guide plates are mounted to and within a mounting block and the mounting block assembly inserted longitudinally into the body chamber.